This invention relates to acetal-protected polymers and photoresist compositions thereof especially useful in 157-nm lithography.
The wavelength of light for lithography has moved to 157-nm to produce the feature size necessary for future electronic devices. Production worthiness of a given resist platform is determined by two important factors: optical transparency and resistance to reactive ion-etching. As in the past, when the wavelength of light required to print is reduced, major modifications in material platform design have to be made at the new wavelength in order to optimize between these two factors. For instance, all phenolic polymers (novolaks and hydroxystyrenes) suitable at g-line, i-line, and 248-nm showed reasonable optical and etching characteristics; however, these materials are highly absorbing at 193-nm. Although aliphatic groups are transparent, they do not have sufficient etch resistance forcing use of alicyclic moieties to improve etch resistance.
At 157-nm, the same barrier to printing features exists in that only a few fluorine and silicon based compounds are transparent. Necessary structural modifications required to produce chemically amplified , resists out of these compounds invariably add to absorbance at 157-nm. Silicon-based resists may have sufficient etch resistance under O2 plasma conditions when used in a bilayer resist design. Fluorine-based resists would require a relatively thick film in order to sustain plasma etch conditions and such film thicknesses may have unacceptably high optical density. Hence, the challenge is to design resist materials, which meet these two conditions. The objective of this present invention is to provide novel polymers based on fluorine and acetal-containing monomer units and their use in photoresist compositions for printing small features at 157-nm.
The invention provides a polymer comprising a fluorine-containing monomer unit, thereby providing a photoresist composition for 157-nm lithography.
The novel polymer comprises at least one acetal-containing monomer unit having the general structure I and at least one of the fluorine-containing monomer units having the general structures II and III: 
wherein R1, R4, R5 and R6 are each independently H, lower alkyl, CH2CO2R10, cyano, CH2CN, or halogen, wherein R10 is any alkyl, cycloalkyl, aryl, arylalkyl, alkylenecycloalkyl, silyl or siloxy or linear or cyclic polysiloxane group; R2 is CHR11R12 where R11 and R12 are each independently H, lower alkyl, cycloalkyl or aryl; A is a substituted or unsubstituted alkylene, cycloalkylene, alkylenecycloalkylene, or alkylenearylene; and R3 is linear, branched or cyclic fluoroalkyl group or SiR13R14R15 where R13, R14, and R15 are each independently an alkyl, cycloalkyl, aryl, arylalkyl, alkylenecycloalkyl, silyl, siloxy, linear or cyclic polysiloxane or silsesquioxane alkyl group; B is an aryl, C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)x where x=0-4, lower alkyl, cycloalkyl, alkene cycloalkyl, silyl, siloxyl, or linear or cyclic polysiloxane group. R7 is H or an acid sensitive group; R8 and R9 are each independently a H or xe2x80x94CN group; and y=0-4.
The present invention also includes a photoresist composition comprising the novel polymer comprising at least one fluorine-containing monomer of Structure II or III or and at least one acetal-containing monomer of Structure I at least one photoacid generator compound, and at least one solvent.
The present invention also includes a silicon-containing resist comprising: a photoresist composition comprising at least one fluorine-containing monomer unit of Structures II or III and at least one acetal-containing monomer unit of Structure I wherein at least one of I, II, and III have a silicon substituent; provided that the silicon substituent is not directly attached to the acetal functionality; at least one photoacid generator compound, and at least one solvent.
The present invention also includes a bilayer resist comprising: a photoresist composition comprising at least one fluorine-containing monomer unit of Structures II or III and at least one acetal-containing monomer unit of Structure I at least one of which has a silicon substituent; provided that the silicon substituent is not directly attached to the acetal functionality, at least one photoacid generator compound, and at least one solvent; and an undercoat layer.